The production of many commercially valuable metals, or metal compounds, from mineral ores includes a process step of digesting the ore with a mineral acid such as hydrofluoric acid. The digesting step is utilized to convert metal species in the mineral ore to metal species which are soluble in aqueous systems so that the metal values may be separated out by selective extractions or the like.
In a typical process, mineral ore concentrates containing tantalum and niobium are conventionally decomposed with hydrofluoric acid (HF) or mixtures of hydrofluoric acid and sulfuric acid (HF/H2SO4). The tantalum and niobium heptafluoro complexes formed are then purified by solvent extraction and separated.
More particularly, in a conventional process for producing tantalum pentoxide (Ta2O5), the tantalum fraction from the ore decomposition is stripped into the aqueous phase and tantalum pentoxide is precipitated using ammonia and recovered by filtration. Niobium pentoxide may be produced in a similar fashion.
Commercial schemes for the extraction and separation of tantalum and niobium values from beneficiated ores or from tin slags are described in detail in U.S. Pat. Nos. 2,767,047; 2,953,453; 2,962,372; 3,117,833; 3,300,297; 3,658, 511; 3,712,939; 4,164,417 and 5,023,059. A general discussion of other ore process schemes is found in Extractive Metallurgy of Niobium, Tantalum and Vanadium, INTERNATIONAL METALS REVIEW, 1984, VOL. 29, NO. 26, BB 405–444 published by The Metals Society (London) and in The Encyclopedia of Chemical Technology, 3rd Ed., Vol. 22 pp. 547–550.
Commercial processing of ores and slags, for example by the processes outlined above, results in ore residues having concentrated levels of metal values not extracted in, or separated by, the processing steps. In particular, ore residues from commercial processes typically have concentrated levels of radioactive metal values. It would be desirable to have a process for separating and recovering the radioactive metal values from ore residues for possible sale, and to generate a residue which may be handled and disposed of as non-radioactive waste. The present invention provides a process which achieves this and other advantageous results.